1. Field of the Invention
The present invention relates to a resin-sealed type semiconductor device in which a semiconductor chip and a part of a lead frame are sealed with a resin, and especially to a one-side sealed type semiconductor device in which a surface of a lead frame on which a semiconductor chip is mounted is sealed with a resin.
2. Description of Related Art
Resin-sealed type semiconductor devices in which a semiconductor chip and a part of a lead frame are sealed with a resin are widely used. Recently, as thin-type apparatus have come into general use, semiconductor devices mounted on these apparatus have also been requested to be thin-type. In conventional resin-sealed type semiconductor devices, generally both of the upper and lower portions of a semiconductor chip and a lead frame in the vicinity thereof are sealed with a resin. However, so-called one-side sealed type semiconductor devices have been developed which are made thin by sealing mainly the upper surface (the surface on which a semiconductor chip is mounted) of a lead frame.
FIG. 7 is a schematic sectional view showing the structure of a conventional one-side sealed type semiconductor device 50.
This semiconductor device 50 comprises a lead frame 51 having a supporting portion 52 and lead terminal portions 53, a semiconductor chip 54 mounted on the supporting portion 52, metal wires 55 for electrically connecting electrodes formed on the upper surface 54a of the semiconductor chip 54 and the upper surfaces 53a of the lead terminal portions 53 respectively, and a sealing resin 56 for sealing the semiconductor chip 54, metal wires 55, and a part of the upper surface of the lead frame 51.
The lead frame 51 has such a structure that the supporting portion 52 is disposed in the central portion thereof, and the lead terminal portions 53 are surrounding the supporting portion 52. The metal wire 55 is electrically connected to the upper surface 53a of the lead terminal portion 53. The lower surface 52b of the supporting portion 52 and the lower surfaces 53b of the lead terminal portions 53 are not coated with the sealing resin 56 but are exposed.
However, in s semiconductor device 50 having such a structure, moisture contained in the atmosphere and the like penetrates into the semiconductor device 50 from a boundary surface between the lead terminal portion 53 and the sealing resin 56 exposed at the bottom surface of the semiconductor device 50. The moisture having penetrated into the semiconductor device 50 travels upwardly along the boundary surface. The moisture having penetrated from below the connecting portion between the lead terminal portion 53 and the metal wire 55 reaches the connecting portion between the lead terminal portion 53 and the metal wire 55. Further, such moisture travels between the metal wire 55 and the sealing resin 56 and reaches an Al pad, which is the electrode formed on the upper surface 54a of the semiconductor chip 54. It has been a problem to be solved that such moisture, containing ions such as Clxe2x88x92, Fe+ and Ni+, causes corrosion through chemical reaction with Al and has a harmful influence on the semiconductor device.
An object of the present invention is to provide a semiconductor device in which moisture penetrating from outside is hard to reach a semiconductor chip, and which has an excellent wet-proof property.
Another object of the present invention is to provide a lead frame to be applied to such a semiconductor device.
A semiconductor device according to the present invention comprises a lead frame having inner connecting portions and outer connecting portions, a semiconductor chip having electrodes on the surface thereof, metal wires for electrically connecting electrodes on the semiconductor chip and the inner connecting portions of the lead frame respectively, a sealing resin for sealing the inner connecting portions of the lead frame, the semiconductor element and the metal wires therein and at the same time exposing the outer connecting portions of the lead frame at the bottom surface thereof, and an inner connecting portion sealing resin for covering the inner connecting portion at the bottom side of the sealing resin.
According to the present invention, the lower portion of the inner connecting portion of the lead frame is covered or coated with the inner connecting portion sealing resin. Therefore, at this portion, the boundary surface of the lead frame and the sealing resin is not exposed, and moisture cannot penetrate into the semiconductor device from this portion. Moisture has to travel a longer distance in order to reach the connecting portion between the inner connecting portion and the metal wire, and accordingly, the traveling distance of moisture becomes the longer in order to reach the semiconductor chip. Therefore, such a semiconductor device has an excellent wet-proof property.
The lead frame may include a supporting portion on which the semiconductor chip is mounted, and lead terminal portions for connecting metal wires. In this case, the supporting portion and the lead terminal portions may be formed at the same height, or the supporting portion may be upset to be higher than the lead terminal portions. When the supporting portion is upset, the sealing resin can be also present below the supporting portion, so that the supporting portion can be firmly held by the sealing resin.
The upper surface area of the supporting portion may be equal to, larger or smaller than the bottom surface area of the semiconductor chip. When the supporting portion is smaller than the semiconductor chip, a larger area of the semiconductor chip is in direct contact with the sealing resin, and thereby detachment of the semiconductor chip from the supporting portion along the boundary surface therebetween can be reduced.
Further, the lead frame is exposed at the position other than the lower portion of the inner connecting portion to form an outer connecting portion. The semiconductor device can be mounted on a wiring substrate or the like by this outer connecting portion.
The end face of the lead frame on the peripheral side may be substantially in the same plane with the side surface of the sealing resin. In such a case, the outer connecting portion does not protrude from the sealing resin, so that the semiconductor device can be small-sized and the area occupied by the semiconductor device, when mounted on a wiring substrate, can be made smaller.
In one embodiment of the present invention, the metal wire is connected to the upper surface of the inner connecting portion, and the lower surface of the inner connecting portion is offset inwardly of the sealing resin with respect to the bottom surface of the sealing resin, while a part of the sealing resin enters in the underside of the inner connecting portion to form the inner connecting portion sealing resin.
With this structure, the inner connecting portion sealing resin is present in a space defined by the lower surface of the inner connecting portion offset inwardly of the sealing resin. Therefore, the bottom surface of the semiconductor device can be a substantially flat surface. Such a semiconductor device can be adequately surface-mounted.
Further, since the inner connecting portion sealing resin is the sealing resin having entered in the underside of the inner connecting portion, these resins are of the same kind. Consequently, these resins can be formed at the same time, thereby to improve productivity.
The inner connecting portion may have such a structure that the upper surface is flat with only the lower surface being offset, or that both of the upper and lower surfaces are offset.
A step may be formed between the lower surface of the outer connecting portion and the lower surface of the inner connecting portion.
Further, a tapered surface, which comes upwardly as it comes inwardly of the sealing resin, may be provided on the lower surface the inner connecting portion.
Such a structure of the inner connecting portion, for example, can be obtained only by machining the head of one end of the lead terminal portion. As a result, the semiconductor device according to the present invention has a simple structure and can be fabricated at a low cost.